﻿<p>The <em>IfcMaterialLayerSet</em> is a designation by which materials of an element constructed of a number of material layers is known and through which the relative positioning of individual layers can be expressed.</p>

<p>The Material Layer Set Base (MlsBase) describes the imaginary axis along which the material layers are positioned.</p>
<ul>
 <li>In case of assigning the <em>IfcMaterialLayerSet</em> directly to an element or element type, the individual layers are stacked 
  according to their position within the list of <em>MaterialLayers</em> without providing information on how to spatially relate the 
  material layer information to the shape representation of the element or element type. </li>
 <li>In case of assigning the <em>IfcMaterialLayerSet</em>  through an <em>IfcMaterialLayerSetUsage</em> to an element, 
  the MlsBase is positioned along the reference axis or reference plane of the element.  An offset from the reference axis or plane to MlsBase is  
  supported by <em>IfcMaterialLayerSetUsage</em> which combines layers and an offset. Offsets from element edges are supported by the subtype  
  <em>IfcMaterialLayerWithOffsets</em>. The positive <em>LayerSetDirection</em> (MlsDirection) describes the direction by which the individual
  material layers are stacked. The <em>IfcMaterialLayer</em>'s are stacked with no gap. Gaps within a material layer set are expressed as layers by
  themselves.</li>
</ul>

<blockquote class="example">EXAMPLE A cavity brick wall would be modeled as <em>IfcMaterialLayerSet</em> consisting of three
<em>IfcMaterialLayer</em>'s: brick, air cavity and brick. The air gap is identified by the <em>IsVentilated</em> flag at
<em>IfcMaterialLayer</em>.</blockquote>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC1.0
</blockquote>

<blockquote class="change-ifc2x4">
IFC4 CHANGE&nbsp; Subtyped from <em>IfcMaterialDefinition</em>, the attribute <em>Description</em>
has been added at the end of attribute list.
</blockquote>

<p class="use-head">Attribute use definition</p>
<p>As shown in Figure 2, each <em>IfcMaterialLayerSet</em> implicitly defines a material
layer set base line (MlsBase), to which the start of the first
<em>IfcMaterialLayer</em> is aligned. The total thickness of a
layer set is calculated from the individual layer thicknesses, the
first layer starting from the MlsBase and following layers being
placed on top of the previous (no gaps or overlaps).</p>

<table>
<tr><td><img src="../../../figures/ifcmateriallayerset-01.png" alt="material layer set" border="0"></td></tr>
<tr><td><p class="figure">Figure 2 &mdash; Material layer set</p></td></tr>
</table>